The present invention is related to electronic circuits, and more particularly to a redundant break before make digital electronic circuit.
Many portable electronic devices utilize a rechargeable battery to provide power. These devices include computers, cellular telephones, pagers, radios, and the like. While there are many types of rechargeable batteries used today, including nickel cadmium and nickel metal hydride, lithium ion batteries have become a popular choice. Lithium ion batteries are typically smaller, lighter, and a have a higher charge capacity than other popular rechargeable battery types.
Typically, to charge a battery, a battery is connected to a charger that is plugged into an AC outlet. During the time the charger is plugged in and the device is in the charger, an indicator light on the charger generally shows the charging status of the battery. For example, the indicator light may flash when the battery is charging and be on constantly when the battery is fully charged. If the user removes the charger plug from the wall with the device still in the charger, the stored charge of the battery may be reduced.
The charging of lithium ion batteries is conducted in a different manner than the charging of nickel type rechargeable batteries. Generally, nickel type rechargeable batteries are charged by applying a constant current until the cell reaches a predetermined voltage or temperature. A lithium ion cell, however, uses a different charging process. First, the lithium ion cell is supplied with a current until the cell""s voltage rises above a threshold. Next, the battery charger is held at the threshold until the current of the cell decreases to a predetermined level.
Therefore, if a battery is charged using a charger not designed specifically for the battery (xe2x80x9cnon-compliant chargerxe2x80x9d) damage to the battery may occur. For example, if a lithium ion battery is placed within a charger designed for a nickel rechargeable battery, the result may be damaging to the battery. The voltage of the lithium ion battery may rise to a dangerous level or overheat. If the battery is overcharged a potential for an explosion of the battery exists.
The present invention is directed at providing a redundant break before make digital circuit. According to one aspect of the invention, redundant circuits are used to create a path to ground for a signal when a fault condition exists.
According to another aspect of the invention, the fault conditions are monitored. The fault condition may be based on characteristics relating to the signal or the chip itself. For example, a fault condition may occur when a temperature measured on the chip exceeds a predetermined threshold. A fault condition may also occur when the signal is above or below a predetermined threshold. For example, a fault condition may occur when the current of the signal is above a predetermined level.
According to yet another aspect of the invention, the state of a switch that couples a cell to a charging path is monitored. When the switch is open and a fault condition has occurred, there are redundant paths to ensure that a switch closes to provide the path to ground during the fault condition.